For obtaining flame-retardant polypropylenes, it is widely carried out to add a flame-retardant composition containing a halogen flame retardant and an antimony compound to various types of polypropylene resin. This is advantageous in that the flame-retardant composition can exhibit flame retardance even when used in a relatively small amount, and hardly detracts from the advantageous performance of polypropylene resins.
However, in a case where such flame-retardant compositions are used, there occurs a problem that a halogen gas is generated in combustion, and therefore use of a halogen-free, that is, so-called non-halogen flame retardant has become investigated.
Regarding the evaluation standards for flame retardance, it is desired that resins themselves are hardly flammable (so-called, self-extinguishing property) and that, in addition thereto, firing or melting resins do not drip or do not drip to spread to fire other substances (so-called drip resistance or drip protection), and recently, a higher flame-retardant level satisfying both self-extinguishing property and drip resistance has become desired.
The recent tendency in the field of automobiles is toward electric vehicles (EV) and hybrid electric vehicles (HEV) and that in the field of home electric appliances is toward induction-heating cookers (IH), and for automobile parts and home electric appliance parts, high-level flame retardance of “V-0” in “UL Standards (US Underwriters Laboratories Standards)-94V” has become desired. In addition, flame-retarding technology in large-size members is being advanced, and flame retardance specialized in self-extinguishing property and drip resistance in a higher level than before is being required. Such flame retardance satisfies an extremely high-level standard of “5VA” in “UL94-5V”.
As in the above, flame-retardant materials are desired for automobile and home electric appliance materials, and these flame-retardant materials are also desired to have mechanical properties on the same level as that of conventional non-flame-retardant materials. Specifically, at present, materials capable of giving an extremely high-level flame retardant effect and capable of satisfying mechanical properties (rigidity, impact), weather resistance and moldability are desired.
PTL 1 describes a flame-retardant resin composition having improved flame retardance by adding a small amount of tetrafluoroethylene resin (PTFE) to a thermoplastic resin to express an effect of drip protection (drip resistance) in firing the thermoplastic resin.
PTLs 2 and 3 describes a technique of imparting mechanical properties, flame retardance and weather resistance by adding glass fibers to a flame-retardant material using a polyolefin and a nitrogen-containing phosphate.